There may be a cam available on the shaft already. See if it has a 2-bolt blank cover or the valve body located on top of the cam box at the flywheel end where Bill's mag is. This is where the air start timing cam is located on many of these engines, and it may work just fine for an OC. With an OC, you won't need no stinkin' air start. You would need to find or fabricate a bracket to hold the mag rigidly in place. A scrap of 1" plate with a slot milled in it for the mag pushrod might work just fine. A couple of "ears" drilled to match the air start valve or block off plate would allow it to mount to the existing holes. You might have to make an extended roller actuator out of a piece of keystock, but I think you could use one from a 4 cycle Superior and just put a keystock spacer in the slot in the back of the mag if needed.